Hindawi Publishing Corporation Advances in Difference Equations Volume 2009, Article ID 830247, 9 pages doi:10.1155/2009/830247 Research Article Multiple Positive Solutions for Nonlinear First-Order Impulsive Dynamic Equations on Time Scales with Parameter Da-Bin Wang and Wen Guan Department of Applied Mathematics, Lanzhou University of Technology, Lanzhou, Gansu, 730050, China Correspondence should be addressed to Da-Bin Wang, wangdb@lut.cn Received 13 February 2009; Accepted 14 May 2009 Recommended by Victoria Otero-Espinar By using the Leggett-Williams fixed point theorem, the existence of three positive solutions to a class of nonlinear first-order periodic b oundary value problems of impulsive dynamic equations on time scales with parameter are obtained. An example is given to illustrate the main results in this paper. Copyright q 2009 D B. Wang and W. Guan. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1. Introduction Let T be a time scale, that is, T is a nonempty closed subset of R.LetT>0 be fixed and 0,T be points in T, an interval 0,T T denoting time scales interval, that is, 0,T T :0,T ∩ T. Other types of intervals are defined similarly. Some definitions concerning time scales can be found in 1–5. In this paper, we are concerned with the existence of positive solutions for the following nonlinear first-order periodic boundary value problem on time scales: x Δ  t   p  t  x  σ  t   λf  t, x  σ  t  ,t∈ J :  0,T  T ,t /  t k ,k 1, 2, ,m, x  t  k  − x  t − k   I k  x  t − k  ,k 1, 2, ,m, x  0   x  σ  T  , 1.1 where λ>0 is a positive parameter, f ∈ CJ × 0, ∞, 0, ∞, I k ∈ C0, ∞, 0, ∞,p: 0,T T → 0, ∞ is right-dense continuous, t k ∈ 0,T T ,0<t 1 < ··· <t m <T,and for each 2 Advances in Difference Equations k  1, 2, ,m,xt  k lim h → 0  xt k  h and xt − k lim h → 0 − xt k  h represent the right and left limits of xt at t  t k . The theory of impulsive differential equations is emerging as an important area of investigation, since it is a lot richer than the corresponding theory of differential equations without impulse effects. Moreover, such equations may exhibit several real world phenomena in physics, biology, engineering, and so forth, see 6–8. At the same time, the boundary value problems for impulsive differential equations and impulsive difference equations have received much attention 9–19. On the other hand, recently, the theory of dynamic equations on time scales has become a new important branch see, e.g., 1–5. Naturally, some authors have focused their attention on the boundary value problems of impulsive dynamic equations on time scales 20–27. In particular, for the first-order impulsive dynamic equations on time scales y Δ  t   p  t  y  σ  t   f  t, y  t   ,t∈ J :  a, b  ,t /  t k ,k 1, 2, ,m, y  t  k   I k  y  t − k  ,k 1, 2, ,m, y  a   η, 1.2 where T is a time scale which has at least finitely-many right-dense points, a, b ⊂ T,pis regressive and right-dense continuous, f : T × R → R is given function, I k ∈ CR, R.The paper 21 obtained the existence of one solution to problem 1.2 by using the nonlinear alternative of Leray-Schauder type. In 22, Benchohra et al. considered the following impulsive boundary value problem on time scales −y ΔΔ  t   f  t, y  t   ,t∈ J :  0, 1  T ,t /  t k , y  t  k  − y  t − k   I k  y  t − k  , y Δ  t  k  − y Δ  t − k   I k  y  t − k  , y  0   y  1   0. 1.3 They proved the existence of one solution to the problem 1.3 by applying Schaefer’s fixed point theorem and the nonlinear alternative of Leray-Schauder type. In 26, Li and Shen studied t he problem 1.3. Some existence results to problem 1.3 are established by using a fixed point theorem, which is due to Krasnoselskii and Zabreiko, and the Leggett-Williams fixed point theorem. In 27, the first author studied the problem 1.1 when λ  1. The existence of positive solutions to the problem 1.1 was obtained by means of the well-known Guo-Krasnoselskii fixed point theorem. Recently, Sun and Li 28 considered the following periodic boundary value problem: x Δ  t   p  t  x  σ  t   λf  x  t  ,t∈  0,T  T , x  0   x  σ  T  . 1.4 Advances in Difference Equations 3 By using the fixed point index, some existence, multiplicity and nonexistence criteria of positive solutions to the problem 1.4 were obtained for suitable λ>0. Motivated by the results mentioned above, in this paper, we shall show that the problem 1.1 has at least three positive solutions for suitable λ>0 by using the Leggett- Williams fixed point theorem 29. We note that for the case λ  1andI k x ≡ 0,k  1, 2, ,m,problem 1.1 reduces to the problem studied by 30. In the remainder of this section, we state the following theorem, which are crucial to our proof. Let E be a real Banach space and K ⊂ E be a cone. A function α : K → 0, ∞ is called a nonnegative continuous concave functional if α is continuous and α  tx   1 − t  y  ≥ tα  x    1 − t  α  y  1.5 for all x, y ∈ K and t ∈ 0, 1. Let a, b > 0 be constants, K a  {x ∈ K : x <a},Kα, a, b{x ∈ K : a ≤ αx, x≤ b}. Theorem 1.1 see 29. Let A : K c → K c be a completely continuous map and α be a nonnegative continuous concave functional on K such that αx ≤x, ∀x ∈ K c . Suppose there exist a, b, d with 0 <d<a<b≤ c such that i {x ∈ Kα, a, b : αx >a} /  φ and αAx >a∀x ∈ Kα, a, b; ii Ax <d∀x ∈ K d ; iii αAx >a,∀x ∈ Kα, a, c with Ax >b. Then A has at least three fixed points x 1 ,x 2 ,x 3 in K c satisfying  x 1  <d, a<α  x 2  ,  x 3  >d with α  x 3  <a. 1.6 2. Preliminaries Throughout the rest of this paper, we always assume that the points of impulse t k are right- dense for each k  1, 2, ,m. We define PC  { x ∈  0,σT  T −→ R : x k ∈ C  J k ,R  ,k  1, 2, ,m and there exist x  t  k  and x  t − k  with x  t − k   x  t k  ,k  1, 2, ,m  , 2.1 where x k is the restriction of x to J k t k ,t k1  T ⊂ 0,σT T ,k  1, 2, ,m and J 0  0,t 1  T ,J m1  σT. Let X  { x  t  : x  t  ∈ PC,x  0   x  σ  T  } 2.2 with the norm x  sup t∈0,σT T |xt|. Then X is a Banach space. 4 Advances in Difference Equations Definition 2.1. A function x ∈ PC ∩ C 1 J \{t 1 ,t 2 , ,t m },R is said to be a solution of the problem 1.1 if and only if x satisfies the dynamic equation x Δ  t   p  t  x  σ  t   λf  t, x  σ  t  every where on J \ { t 1 ,t 2 , ,t m } , 2.3 the impulsive conditions x  t  k  − x  t − k   I k  x  t − k  ,k 1, 2, ,m, 2.4 and the periodic boundary condition x0xσT. Lemma 2.2. Suppose h : 0,T T → R is rd-continuous, then x is a solution of x  t   λ  σT 0 G  t, s  h  s  Δs  m  k1 G  t, t k  I k  x  t k  ,t∈  0,σT  T , 2.5 where G  t, s   ⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩ e p  s, t  e p  σ  T  , 0  e p  σ  T  , 0  − 1 , 0 ≤ s ≤ t ≤ σ  T  , e p  s, t  e p  σ  T  , 0  − 1 , 0 ≤ t<s≤ σ  T  , 2.6 if and only if x is a solution of the boundary value problem x Δ  t   p  t  x  σ  t   λh  t  ,t∈ J :  0,T  T ,t /  t k ,k 1, 2, ,m, x  t  k  − x  t − k   I k  x  t − k  ,k 1, 2, ,m, x  0   x  σ  T  . 2.7 Proof. Since the method is similar to that of in 27, Lemma 3.1, we omit it here. Lemma 2.3. Let Gt, s be defined as Lemma 2.2,then 1 e p  σ  T  , 0  − 1 ≤ G  t, s  ≤ e p  σ  T  , 0  e p  σ  T  , 0  − 1 ∀t, s ∈  0,σT  T . 2.8 Proof. It is obvious, so we omit it here. Let K  { x  t  ∈ X : x  t  ≥ δ  x  } , 2.9 where δ  1/e p σT, 0 ∈ 0, 1. It is not difficult to verify that K is a cone in X. Advances in Difference Equations 5 We define an operator Φ : K → X by  Φx  t   λ  σT 0 G  t, s  f  s, x  σ  s  Δs  m  k1 G  t, t k  I k  x  t k  ,t∈  0,σT  T . 2.10 By 27, Lemmas 3.3 and 3.4,itiseasytoseethatΦ : K → K is completely continuous. 3. Main Result Notation 1. Let f 0  lim x → 0 sup max t∈0,T T f  t, x  x ,I 0  lim x → 0 sup m  k1 I k  x  x , f ∞  lim x →∞ sup max t∈0,T T f  t, x  x ,I ∞  lim x →∞ sup m  k1 I k  x  x , 3.1 and for μ>0, we define I μ  min δμ≤x≤μ  m k1 I k x. Theorem 3.1. Assume that there exists a number b>0 such that the following conditions: H 1  ft, x >e p σT, 0x − e p σT, 0/e p σT, 0− 1I b ≥ 0 for δb ≤ x ≤ b, t ∈ 0,T T ; H 2  f 0  I 0 < e p σT, 0 − 1/e p σT, 0,f ∞  I ∞ < e p σT, 0 − 1/e p σT, 0 hold. Then the problem 1.1 has at least three positive solutions for e p  σ  T  , 0  − 1 σ  T  e p  σ  T  , 0  <λ< 1 σ  T  . 3.2 Proof. Let αxmin t∈0,σT T xt, it is easy to see that αx is a nonnegative continuous concave functional on K such that αx ≤x, ∀x ∈ K c . First, we assert that there exists c>bsuch that Φ : K c → K c is completely continuous. In fact, by the condition f ∞  I ∞ < e p σT, 0 − 1/e p σT, 0 of H 2 , there exist C 0 >b,and 0 <ε<e p σT, 0 − 1/e p σT, 0 − f ∞  I ∞ /2 such that f  t, x  ≤  ε  f ∞  x, m  k1 I k  x  ≤  ε  I ∞  x, for x>C 0 . 3.3 6 Advances in Difference Equations Let C 1  C 0 /δ, if x ∈ K, x >C 1 , then x>C 0 and we have  Φx  t   λ  σT 0 G  t, s  f  s, x  σ  s  Δs  m  k1 G  t, t k  I k  x  t k  ≤ λ e p  σ  T  , 0  e p  σ  T  , 0  − 1  σT 0  ε  f ∞   x  Δs  e p  σ  T  , 0  e p  σ  T  , 0  − 1  ε  I ∞   x    λ e p  σ  T  , 0  e p  σ  T  , 0  − 1 σ  T   ε  f ∞   e p  σ  T  , 0  e p  σ  T  , 0  − 1  ε  I ∞    x  <  x  . 3.4 Take K C 1  {x | x ∈ K, x≤C 1 }, then the set K C 1 is a bounded set. According to that Φ is completely continuous, then Φ maps bounded sets into bounded sets and there exists a number C 2 such that  Φx  ≤ C 2 for any x ∈ K C 1 . 3.5 If C 2 ≤ C 1 , we deduce that Φ : K C 1 → K C 1 is completely continuous. If C 1 <C 2 , then from 3.4, we know that for any x ∈ K C 2 \ K C 1 , x >C 1 and Φx < x≤C 2 hold. Then we have Φ : K C 2 → K C 2 is completely continuous. Take c  max {C 1 ,C 2 }, then c>band Φ : K c → K c are completely continuous. Second, we assert that {x ∈ Kα, δb,b : αx >δb} /  φ and αAx >δbfor all x ∈ Kα, δb, b. In fact, take x ≡ b  δb/2, so x ∈{x ∈ Kα, δb, b : αx >δb}. Moreover, for x ∈ Kα, δb, b, then αx ≥ δb and we have α  Φx   min t∈0,σT T  λ  σT 0 G  t, s  f  s, x  σ  s  Δs  m  k1 G  t, t k  I k  x  t k   ≥ λ e p  σ  T  , 0  − 1 · σ  T   e p  σ  T  , 0  α  x  − e p  σ  T  , 0  e p  σ  T  , 0  − 1 I b   1 e p  σ  T  , 0  − 1 I b >α  x  ≥ δb. 3.6 Third, we assert that there exist 0 <d<δbsuch that Φx <dif x ∈ K d . Indeed, by the condition f 0  I 0 < e p σT, 0 − 1/e p σT, 0 of H 2 , there exist 0 <d<δb,and 0 <ε<e p σT, 0 − 1/e p σT, 0 − f 0  I 0 /2 such that f  t, x  ≤  ε  f 0  x, m  k1 I k  x  ≤  ε  I 0  x, for 0 ≤ x ≤ d. 3.7 Advances in Difference Equations 7 Then x ∈ K d , we get  Φx  t   λ  σT 0 G  t, s  f  s, x  σ  s  Δs  m  k1 G  t, t k  I k  x  t k  ≤ λ e p  σ  T  , 0  e p  σ  T  , 0  − 1  σT 0  ε  f 0  x  s  Δs  e p  σ  T  , 0  e p  σ  T  , 0  − 1  ε  I 0  x ≤  λ e p  σ  T  , 0  e p  σ  T  , 0  − 1  ε  f 0  σ  T   e p  σ  T  , 0  e p  σ  T  , 0  − 1  ε  I 0    x  < e p  σ  T  , 0  e p  σ  T  , 0  − 1  f 0  I 0  2ε   x  <  x  <d. 3.8 Finally, we assert that αΦx >δbif x ∈ Kα, δb, c and Φx >b. To do this, if x ∈ Kα, δb, c and Φx >b,then α  Φx  ≥  Φx  t  ≥ δ  Φx  >δb. 3.9 To sum up, all the hypotheses of Theorem 1.1 are satisfied by taking a  δb. Hence Φ has at least three fixed points, that is, the problem 1.1 has at least three positive solutions x 1 ,x 2 and x 3 such that  x 1  <d,a<α  x 2  ,  x 3  >dwith α  x 3  <a. 3.10 Corollary 3.2. Using (H 3 ) f 0  I 0  f ∞  I ∞  0, instead of (H 2 )inTheorem 3.1, the conclusion of Theorem 3.1 remains true. 4. Example Example 4.1. Let T 0, 1 ∪ 2, 3. We consider the following problem on T : x Δ  t   x  σ  t   λf  t, x  σ  t  ,t∈  0, 3  T ,t /  1 2 , x  1 2   − x  1 2 −   I  x  1 2  , x  0   x  3  , 4.1 8 Advances in Difference Equations where λ>0 is a positive parameter, pt ≡ 1,T  3,m 1, and f  t, x   ⎧ ⎨ ⎩ 9e 6  t  1  x 2 ,  0, 1  , 9e 6  t  1  x 1/2 ,  1, ∞  , I  x   ⎧ ⎨ ⎩ x 2 ,  0, 1  , x 1/2 ,  1, ∞  . 4.2 Taking b  1, then by δ  1/2e 2  it is easy to see that I b  min δb≤x≤b Ix1/4e 4 . So, ∀x ∈ δb, b1/2e 2 , 1, we have ft, x ≥ 9/4e 2  > 2e 2 − 1/2e 2 − 12e 2  ≥ 2e 2 x − 2e 2 /2e 2 − 11/4e 4 e p σT, 0x − e p σT, 0/e p σT, 0 − 1I b . Obviously, we have f 0  I 0  f ∞  I ∞  0. Therefore, together with Corollary 3.2, it follows that the problem 4.1 has at least three positive solutions for 2e 2 − 1/6e 2  <λ<1/3. 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